1. Field of the Invention
The present invention relates generally to an optical disk apparatus including an optical disk drive mechanism and a circuit board mounted with a control circuit and, more particularly, to an optical disk apparatus constructed to decrease a thickness of the apparatus.
2. Description of the Related Art
An optical disk apparatus has been utilized as a storage apparatus in a computer system. Such an optical disk apparatus has been required to increase in storage capacity and to be downsized. For example, it has been required that the optical disk apparatus be incorporated into a lap-top type computer.
FIG. 6 is a view showing a construction in the prior art. FIG. 7 is a block diagram showing a circuit in the prior art. FIGS. 6 and 7 exemplify a magneto-optic disk apparatus by way of an optical disk apparatus.
As illustrated in FIG. 6, a control circuit of the magneto-optic disk apparatus is constructed as follows. To be specific, a microprocessor (MPU) 61 executes main control of the apparatus. A random access memory (RAM) 65 is a memory used for processing of the MPU 61.
A read-only memory (ROM) 66 is a memory for storing the control program executed by the MPU 61. An optical disk controller (ODC) 63 carries out the interface control with a host apparatus, and also encodes/decodes the data. A random access memory (RAM) 67 is used as a buffer memory for read/write data.
A digital signal processor (DSP) 64 effects servo control of the optical head of the optical disk drive mechanism. A control logic circuit 62 is a group of logic circuits for transmitting and receiving digital signals to and from the optical head of the optical disk drive mechanism. The control logic circuit 62 creates a timing gate signal for transmitting and receiving the data between the optical head and the processor 61.
Such digital circuits 61, 65, 63, 64, 66 are connected via a common address/data bus 68. Analog circuits are provided in addition to these digital circuits. The analog circuits consist of a read circuit 69, a write circuit 71, a drive circuit 72 and a signal amplifier circuit 75.
The read circuit 69 amplifies an output of an optical detector 90 of the optical head and thereafter generates data pulses. The thus generated pulses are outputted as read data to a controller 63. The write circuit 71 pulse-drives a laser diode 91 of the optical head with a predetermined power in accordance with the write data. The data are thereby written onto the optical disk.
The drive circuit 72 drives the drive mechanism 92 of the optical head in accordance with a servo signal given from the DSP 64. The drive mechanism 92 of the optical head may include a focus actuator of the optical head, a track actuator of the optical head, and a moving motor of the optical head.
A servo AGC circuit 81 creates a focus error signal and a track error signal from detection outputs of the optical detector 90 within the optical head, and outputs them to the DSP 64.
An explanation will be given with reference to a circuit block diagram of FIG. 7.
As illustrated in FIG. 7, the MPU 61 and the control logic circuit 62 are formed on one chip. Then, a clock source 73 is connected to this one-chip LSI. The RAM 67 and a terminal resistor 74 of a host interface are connected to the optical disk controller 63. The RAM 65 and the ROM 66 are connected to the MPU 61 via the address/data bus 68.
The optical head 80 is provided with a write LSI circuit 71 and a pre-amplifier servo AGC circuit 81. The write LSI circuit 71 performs read/write light emission control of the laser diode (light emitting element) 91. The write LSI circuit 71 is connected to the control logic circuit 62, and performs read/write light emission control of the laser diode 91 in accordance with an indication from the MPU 61.
After converting a detection current of the optical detector 90 of the optical head 80 into a voltage, the pre-amplifier servo AGC circuit 81 generates a regenerative signal, a focus error signal and a track error signal. The focus/track error signals are outputted to the DSP 64.
The read circuit (LSI) 69 generates a data pulse from of the regenerative signal of the pre-amplifier servo AGC circuit 81, and outputs the pulsed read data to the optical disk controller 63. Note that an analog switch 69-1 and an inverting circuit 69-2 are provided for the read circuit 69.
The analog LSI circuit 75 is constructed by integrating analog circuits such as an operational amplifier and a comparator that are used within the apparatus. The analog LSI circuit 75 filters and amplifies the focus/track error signals.
An amplifier 76 is an operational amplifier for analog filtering. The amplifier 76 filters an output of the pre-amplifier servo AGC circuit 81. An amplifier 77 is an operational amplifier for analog filtering and further filters the output from the analog LSI circuit 75.
A mechanism 82 of the optical disk drive is provided with a lens position detecting circuit 93 for detecting a lens position of the optical head 80. An AGC amplifier 70 is a circuit for effecting a current/voltage conversion of a sensor signal of the detecting circuit 93.
Further, the mechanism 82 of the optical disk drive is provided with a focus actuator 92-1, a track actuator 92-2 and a voice coil motor 92-3 as drive mechanisms of the optical head 80.
The focus actuator 92-1 drives the lens of the optical head 80 in a focusing direction, thereby adjusting a focus position of light beams. The track actuator 92-2 drives the lens of the optical head 80 in a track traversing direction, thereby adjusting a track position of the light beams. The voice coil motor 92-3 moves the optical head 80 in the track traversing direction on the optical disk.
The DSP 64 executes a variety of servo control processes in response to the focus/track error signals transmitted from the analog LSI circuit 75, and the lens position detecting signal from the AGC amplifier 70. That is to say, the DSP 64 performs focus servo control, track servo control and seek control as well.
The DSP 64 has a group of A/D converters for executing analog-to-digital conversions of the focus/track error signals and the lens position detecting signal. Then, the DSP 64 calculates servo control values (a focus servo control value, a track servo control value and a seek servo control value) on the basis of these A/D converted signals.
The DSP 64 has a group of D/A converters for converting the various servo control values into analog servo control values. A drive circuit 72 for the servo control and the seek control is connected to the DSP 64.
This drive circuit 72 is constructed of a focus driver circuit 72-1 for driving the focus actuator 92-1 in accordance with a focus servo control quantity, a track driver circuit 72-2 for driving the track actuator 92-2 in accordance with a track servo control quantity, and a VCM driver circuit 72-3 for driving a voice coil motor 92-3 in accordance with a seek servo control quantity.
Further, the mechanism 82 is provided with an eject motor 93-1 for ejecting the optical disk cartridge out, and a spindle motor 93-2 for rotating the optical disk.
The eject driver circuit 78-1 drives the eject motor 93-1 in accordance with an indication of the MPU 61 via the control logic circuit 62. The spindle driver circuit 78-2 drives a spindle motor 93-2 in accordance with an indication of the MPU 61 through the control logic circuit 62.
Provided further is a bias magnetic field coil 94 for applying a magnetic field across the optical disk. The bias driver circuit 79 drives the bias magnetic field coil 94 in accordance with an indication of the MPU 61 via the control logic circuit 62. The bias magnetic field coil 94, through which predetermined currents in positive and negative directions flow, thereby generates the magnetic fields of positive and negative polarities.
An amplifier 79-1 is an operational amplifier for detecting the bias drive current. A comparator 79-2 is a comparator for setting a bias drive current value.
A dip switch 75 is a switch for setting addresses from outside. A flip-flop 76 holds set values of the dip switch 75. The dip switch 75 and the flip-flop 76 are provided for an SCSI interface.
FIGS. 8 and 9 are diagrams (part 1, and part 2) showing a construction in the prior art. FIG. 10 is a diagram illustrating a construction in the prior art.
FIG. 8 is the diagram of a circuit board 86 as viewed from above. FIG. 9 is the diagram of the circuit board 86 as viewed from under. According to the prior art, as illustrated in FIG. 8, respective ICs and LSIs are mounted on the upper surface of the single circuit board 86. Then, remaining ICs and LSIs 65, 66, 67-2 are mounted on the lower surface of the circuit board 86 is, as illustrated in FIG. 9. Incidentally, 84-1 to 84-5 in FIGS. 8 and 9 designate connectors for connections to the optical disk drive mechanism. Additionally, the numeral 85 represents an interface connector consisting of an SCSI interface connector.
Referring to FIG. 9, areas 87, 88, 89 defined by dotted lines on the circuit board 86 are classified as wiring areas for an address/data bus, etc. The areas elevated by the bias coils of the optical disk drive mechanisms 80, 82 do not have a height enough to mount the parts. Parts can not be mounted on these areas and these areas are therefore provided with the address/data bus.
As shown in FIG. 10, the circuit board 86 is fixed onto the optical disk drive mechanism 82 with screws. The circuit board 86 is fixed to the optical disk drive mechanism 82 so that its lower surface, upon which is mounted a comparatively small number of parts, faces to the optical disk drive mechanism 82.
In recent years, there has been demanded an expansion of a field where the optical disk apparatus is utilized. The optical disk apparatus is required to be used as a substitute for, e.g., a floppy disk apparatus of a lap-top type computer. The lap-top type computer has a slot for a 3.5 inch. floppy disk apparatus that is approximately 17 mm thick, 102 mm wide and 140 mm deep.
Accordingly, it is required that the optical disk apparatus be constructed of a size small enough to enter this slot in order to incorporate the optical disk apparatus into the lap-top type computer.
There arises, however, a problem inherent in the prior art, wherein both surfaces of the circuit board 86 are mounted with the parts such as ICs in the prior art, and hence the optical disk apparatus can not be reduced in thickness.
Further, the control circuit of the optical disk apparatus has a multiplicity of digital LSIs connected to a common bus. Then, these components are connected to each other via the common bus, and therefore the bus on the circuit board needs to be made relatively long. The common bus can not be normally arranged at random, but is required to be arranged in parallel. Therefore, the bus on the circuit board is a large obstacle against the layout of the parts. Another problem is that it is difficult to mount a one-sided surface of a small circuit board with the parts.
Furthermore, a multiplicity of analog circuits exist in the control circuits of the optical disk apparatus. Those analog circuits are not so resistant to outside noises. On the other hand, since the digital circuit makes high-frequency signals run through the common bus, the noises are caused from the bus. There must be a problem in which those noises exert adverse influences on the analog circuits mounted on the circuit board.
Besides, the circuit board is required to be mounted with the multiplicity of ICs, and this mounting is time-consuming. Moreover, both surface of the circuit board are mounting with and parts, and therefore are required to be reflow-soldered. This results in such a problem that the manufacturing costs increase.